The present invention relates generally to micro-pumps, and more particularly to a micro-pump that utilizes electrostatic forces to create a peristaltic deformation in a viscoelastic material disposed in the passageway of a pump body to precisely pump small quantities of liquids.
Various types of micro-pumps are known for pumping a controlled flow of a small quantity of liquid. Such micro-pumps find particular use in fields such as analytical chemistry wherein an accurate and measured control of a very small liquid flow is required. Such micro-pumps are also useful in the medical field for regulating precise flows of small amounts of liquid medications.
Many prior art micro-pumps utilize electromechanical mechanisms which while effective are relatively complex and expensive to manufacture on the small scales necessary to control small fluid flows. For example, micro-pumps utilizing piezoelectric materials are known wherein a pump element is oscillated by the application of electrical impulses on piezoelectric crystals to create a pressure differential in a liquid. Unfortunately, piezoelectric crystals are formed from brittle, ceramic materials which are difficult and expensive to machine, particularly on small scales. Additionally, piezoelectric materials generally are not suitable for interfacing with liquids. Thus, micro-pumps that exploit piezoelectric movement must be designed to insulate the piezoelectric crystals from contact with liquid materials. Finally, piezoelectric materials generally cannot be fabricated by way of known CMOS processes. Hence, while the electrical circuitry necessary to drive and control piezoelectric movement with a micro-pump may be easily and cheaply manufactured by CMOS processes, the integration of the piezoelectric materials into such circuits requires relatively specialized and slow fabrication steps.
Clearly, there is a need for a micro-pump which is capable of inducing a precise flow of a small amount of a liquid without the need for relatively expensive and difficult to machine materials. Ideally, all of the components of such a micro-pump could be manufactured from relatively inexpensive, easily-worked with materials which are compatible both with contact with liquid and with CMOS manufacturing techniques.
A main aspect of the invention is the provision of an electrostrictive micro-pump for pumping a controlled amount of fluid that overcomes or at least ameliorates all of the aforementioned shortcomings associated with the prior art. The micro-pump of the invention comprises a pump body having a passageway for conducting a flow of fluid, a pump element formed from apiece of viscoelastic material and disposed in the passageway, and a control assembly coupled with the viscoelastic material for inducing an elastic deformation in the shape of the material that creates a pressure differential in fluid disposed in the pump body passageway.
The control assembly may include a pair of electrodes disposed on opposite sides of the viscoelastic material, a source of electrical voltage connected to the electrodes, and a switching circuit for selectively applying a voltage from the source across the electrodes to generate an electrostatic force therebetween that deforms the viscoelastic material. One of the electrodes may be a flexible electrically conducting coating disposed over an upper, fluid contacting side of the viscoelastic material, while the other electrode is preferably a plurality of conductive panels uniformly spaced over a lower, opposing side of the viscoelastic material that is mounted in the passageway of the pump body. The switching circuit preferably includes a multiplexer for sequentially applying voltage from the voltage source to the conductive panels of the lower electrode to induce a peristaltic deformation in the viscoelastic material along the pump body passageway.
The viscoelastic material forming the pump element may be a silicon elastomer. Additionally, the electrodes of the control assembly are preferably formed from a coating of a conductive metal, such as gold, silver, or nickel, or a conductive polymer such as poly pyrrole, polyanaline, or poly thiophene. Alternatively, the conductive coating forming either of the electrodes may be formed from diamond-like carbon. In all cases, the coatings are thin enough so as not to interfere with the desired, peristaltic deformation of the viscoelastic material upon the application of a voltage.
The electrostrictive micro-pump of the invention is fabricated from relatively inexpensive and easily worked with materials, and the electrode structure of the control assembly may be easily manufactured by CMOS technology. The inherent elastic properties of commercially available viscoelastic materials advantageously allow for peristaltic movements of the valve element at accurately controllable frequencies up to 12.5 kHz.